The present invention relates to a fibrous backing sheet for a surface covering. More particularly, the invention relates to a backing sheet which includes a coating of substantial thickness. Preferably, the coating is a highly filled, hydrophylic, resinous binder.
It is known to apply coatings to the fibrous material forming a backing sheet for a surface covering such as a floor. For example, see Grose U.S. Pat. No. 4,274,961. At column 9, lines 23 to 33, Grose states that fibrous backing sheet material often has a size or leveling coat applied to its surface prior to the application of one or more resinous polymeric compositions. He indicates that such a coat serves as a barrier coat preventing the migration of any of the impregnant or binder in the fibrous backing material into the overlying resinous polymer compositions. Further, he states the size coat often serves to provide good adhesion between the fibrous base backing material and the resinous polymeric composition.
However, Grose does not teach or suggest the use of a substantially thick coating. The size or leveling coats of the prior art are thin because the binder comprising the coat is expensive relative to the fibrous material of the backing sheet.
Further, Grose makes no mention of a filler in the coating composition. Rather, at column 9, lines 34 to 41, he states that the compositions are usually polyvinyl chloride homopolymers or copolymers. Such compositions are hydrophobic and are applied to deter water absorption by the fibrous sheet of asbestos or cellulosic fibers forming the backing sheet. Such water absorption leads to swelling and dimensional instability of the backing sheet.
European Patent Application 227,853 is directed to non-woven, fibrous composite materials in sheet form which are particularly useful as dimensionally stable backings and inner liners for surface covering laminates. As typical of the prior art, at page 13, lines 15 to 19, EPA 227,853 discloses a sizing or coating having nominal thickness of from about 0.1% to about 1% of the sheet. The sizing is a hard cationic acrylic latex which is applied to both sides of the composite sheet. There is no teaching or suggestion of a filler in the coating composition.
Highly filled sheets for use in floor coverings have been used such as disclosed in McReynolds U.S. Pat. No. 4,225,383. However, the high filler loading (60% to 95%) is part of the layer of fibrous material and not a coating. There is no teaching or suggestion in McReynolds of coating the fibrous layer.
Bondoc U.S. Pat. No. 4,373,992 also discloses a typical backing sheet composition which includes glass fibers, cellulosic fibers, synthetic organic fibers, inorganic filler, binder and calcium hydroxide. However, once again, there is no mention of coating the fibrous layer.
Cellulose fibers have been generally substituted by the floor covering industry for asbestos fibers which were previously used to form the backing felt in flooring structures. However, cellulose has a number of disadvantages including being hydroscopic. This leads to water absorption and dimensional instability.
Most flooring felt is "sized;", i.e., coated with a thin layer of binder to reduce the generation of dust during manufacture. The binder is hydrophobic which helps to improve water resistance but does not add substantially to the caliper or thickness of the felt. However, this hydrophobicity creates difficulties in adhering the flooring structure to the floor since most adhesives are water based.
One object of the present invention is to provide a coated fibrous backing sheet for a surface covering which maintains dimensional stability and yet improves compatability with water based adhesives to improve the adhesive bond or glueability.